From 35fa5074aa256880f70591eb656dceeb1a7feae0 Mon Sep 17 00:00:00 2001
From: Gabe Black <gblack@eecs.umich.edu>
Date: Mon, 4 Jun 2012 10:43:09 -0700
Subject: [PATCH] X86: Ensure that the CPUID instruction always writes its
 outputs.

The CPUID instruction was implemented so that it would only write its results
if the instruction was successful. This works fine on the simple CPU where
unwritten registers retain their old values, but on a CPU like O3 with
renaming this is broken. The instruction needs to write the old values back
into the registers explicitly if they aren't being changed.
---
 src/arch/x86/isa/decoder/two_byte_opcodes.isa | 17 ++++++++++++-----
 src/arch/x86/isa/formats/cpuid.isa            |  5 +----
 2 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/src/arch/x86/isa/decoder/two_byte_opcodes.isa b/src/arch/x86/isa/decoder/two_byte_opcodes.isa
index 34b79a6a4..3b187d625 100644
--- a/src/arch/x86/isa/decoder/two_byte_opcodes.isa
+++ b/src/arch/x86/isa/decoder/two_byte_opcodes.isa
@@ -721,12 +721,19 @@
                 0x1: pop_fs();
                 0x2: CPUIDInst::CPUID({{
                     CpuidResult result;
-                    success = doCpuid(xc->tcBase(), bits(Rax, 31, 0),
+                    bool success = doCpuid(xc->tcBase(), bits(Rax, 31, 0),
                         bits(Rcx, 31, 0), result);
-                    Rax = result.rax;
-                    Rbx = result.rbx;
-                    Rcx = result.rcx;
-                    Rdx = result.rdx;
+                    if (success) {
+                        Rax = result.rax;
+                        Rbx = result.rbx;
+                        Rcx = result.rcx;
+                        Rdx = result.rdx;
+                    } else {
+                        Rax = Rax;
+                        Rbx = Rbx;
+                        Rcx = Rcx;
+                        Rdx = Rdx;
+                    }
                     }});
                 0x3: Inst::BT(Ev,Gv);
                 0x4: Inst::SHLD(Ev,Gv,Ib);
diff --git a/src/arch/x86/isa/formats/cpuid.isa b/src/arch/x86/isa/formats/cpuid.isa
index cc3070ded..535f1e925 100644
--- a/src/arch/x86/isa/formats/cpuid.isa
+++ b/src/arch/x86/isa/formats/cpuid.isa
@@ -73,13 +73,10 @@ def template CPUIDExecute {{
     {
         // If the CPUID instruction used a valid function number, this will
         // be set to true. Otherwise, the instruction does nothing.
-        bool success;
         %(op_decl)s;
         %(op_rd)s;
         %(code)s;
-        if (success) {
-            %(op_wb)s;
-        }
+        %(op_wb)s;
         return NoFault;
     }
 }};